1. Field of the Invention
The present invention relates in general to blown film extrusion lines, and specifically to collapsing frames for use in blown film extrusion lines.
2. Description of the Prior Art
Blown film extrusion lines are utilized to produce plastic products, such as plastic bags and plastic sheets. While the output of these blown film-extrusion lines is relatively inexpensive material, the lines are expensive to purchase and expensive to operate. Typically, blown film extrusion lines produce large quantities of product. The costs associated with down time of the blown film extrusion line can amount to thousands of dollars per hour. The same is true for extrusion lines which produce product which is out of specification. Typically, the product which is generated by blown film extrusion lines must satisfy some fairly tight constraints. The diameter of the product should be uniform and the thickness of the product should be uniform. There are numerous prior art references which teach systems for gaging and controlling the circumference of an extruded film tube, including several prior art references which are commonly owned by Applicant. However, there has been very little effort in the prior art to better control the operation of the collapsing frames which serve to collapse the extruded film tube and flatten it. The present invention is directed to better control of the collapsing frame.
It is one objective of the present invention to provide an improved extruded film apparatus which includes a control mechanism for gaging and controlling the diameter of the extruded film tube, and a control mechanism for controlling the position of the boards which are present in the collapsing frame and which serve to collapse and flatten the extruded film tube before it is fed to rollers for further processing.
It is another objective of the present invention to provide a control system for the collapsing frame of an extruded film tube apparatus, wherein the boards associated with the collapsing frame have their position monitored by a non-contact ultrasonic transducer which determines whether the boards are either too far in or too far out relative to a predetermined set position. The invention further includes actuators for moving the boards associated with the collapsing frame either inward or outward in response to the position as determined by the position sensors.
These and other objectives are achieved as is now described. The present invention is directed to an improved blown film extrusion apparatus. An annular die is provided for extruding a film tube. At least one tube position transducer is located adjacent the extruded film tube for transmitting interrogating pulses to the extruded film tube and for producing a position signal corresponding to a detected position of the extruded film tube. A bubble position control system is provided for receiving and processing the position signal. A means is provided for varying the quantity of air within the extruded film tube in response to the bubble position and control means for for urging the extruded film tube to a desired position. A collapsing frame assembly is provided for receiving the extruded film tube and collapsing the extruded film tube. The collapsing frame assembly includes a plurality of frame boards. It further includes at least one board position transducer for detecting the position of at least one of the plurality of frame boards. The collapsing frame assembly further includes at least one board position actuator for adjusting the position of at least one of the plurality of frame boards. A board control system is provided for receiving board position information from the board position transducer and for passing control signals to the board position actuator to maintain at least one of the plurality of frame boards in a predetermined position.
The above as well as additional objectives, features, and advantages will become apparent in the following description.